NewBlindSignatureContext creates the data needed to send to a signer to complete a blinded signature `msgs` is an index to message map where the index corresponds to the index in `generators` msgs are hidden from the signer but can also be empty if no messages are hidden but a blind signature is still desired because the signer should have no knowledge of the signature.

NewPokSignature creates the initial proof data before a Fiat-Shamir calculation.

BlindSignature is a BBS+ blind signature structurally identical to `Signature` but is used to help avoid misuse and confusion.

BlindSignatureContext contains the data used for computing a blind signature and verifying proof of hidden messages from a future signature holder.

MessageGenerators are used to sign a vector of commitments for a BBS+ signature.

PokSignature a.k.a.

PokSignatureProof is the actual proof sent from a prover to a verifier that contains a proof of knowledge of a signature and the selective disclosure proof.

PublicKey is a BBS+ verification key.

SecretKey is a BBS+ signing key.

Signature is a BBS+ signature as described in 4.3 in <https://eprint.iacr.org/2016/663.pdf>.